The present invention relates to the stator windings of large dynomoelectric machines such as turbine generators, and more particularly, to the insulation and mechanical support of the stator coil ends of such machines.
Large turbine generators are usually of the inner cooled, or direct cooled, construction in which a coolant fluid is circulated through duct means in the stator and rotor slots in direct thermal relation with the current-carrying conductors inside the ground insulation. This type of construction provides a very effective cooling system which has made it possible to obtain the high capacities required in large generators without exceeding the permissible limits of physical size. In most cases, the coolant fluid used in hydrogen which fills the gas-tight housing of the machine and is circulated by a blower on the rotor shaft through the ducts of the rotor and stator windings and through radial or axial ducts in the stator core. The stator windings of these machines are made up of stranded conductors disposed in the slots of the stator core and suitably connected at their ends to form complete coils. The conductors are cooled by means of ventilating ducts which are arranged in either one or two stacks disposed between columns of conductor strands and which extend throughout the length of the conductor in the stator slots and the ends portions. The ends of the ducts extend outward from the conductors and are open for circulation of the coolant gas.
In the usual arrangement, two conductors are placed in each slot of the stator core and the ends of each conductor extend beyond the core and are formed in a complex curve extending around the core and terminating in an end portion adjacent to the end portion of another conductor lying in a different slot. These adjacent conductor end portions are connected together to form complete coils which are suitably connected to form the stator winding. In many cases, especially where two stacks of ventilating ducts are used in each conductor, the stator coil extreme end portions and the end connections between conductors have been left uninsulated, since these portions of the coil are well removed from the grounded core. The reason for this has been primarily to facilitate ventilation and to allow easy inspection of the soldered connections between conductors which include group transpositions of the stranded conductors. Failures of the connections and end turn portions have occurred, however, which are due in many cases to vibration and fatigue which may cause breaking of some of the strands leading to an electrical failure. Other types of mechanical failures have also occurred and better mechanical strength and reinforcement of these connections and coil end portions are needed. An insulating cover is also desirable for the exposed ends of the metal ventilating ducts.